Arthur C Clarke and 'The Sentinel'
The Arthur C Clarke story 'The Sentinel' (remote 'ancestor' of his film 2001: A Space Odyssey) has moon explorers finding life on the moon
'The only living things that had ever existed there were a few primitive plants and their slightly less degenerate ancestors.'
I remember thinking when I read it as a kid that it was unlikely as the Moon could never have had an atmosphere. Seems I was wrong.